1. Technical Field
The invention relates to art of precision machining crank pins of crankshafts for internal combustion engines and, more particularly, to such machining carried out by rotating the crankshaft with its pins in machining contact with tools that are substantially non-rotating with respect to the pin axis.
2. Description of the Prior Art
In the case of a previously employed apparatus of this type, tools are used which have a bearing portion which presents a dimensionally stable arcuate surface or half-shell and is often rotationally movable with respect to a displacement cylinder associated therewith. The bearing portions are arranged on a plurality of supports or guide shoes spaced apart from one another in the peripheral direction of the surface of the shell. The bearing portion may preferably consist of plastic material in the form of a honing belt. The honing belt permits precision machining of the associated crank pin of a workpiece and has the potential to increase the bearing portion and facilitate the rounding of the edges of lubricating oil bores already formed in rough-machined crank pins.
For this type of apparatus, an alternative use of tools is also known in which, instead of working with a honing belt, the precision machining of the crank pins is carried out with one or more honing stones in a manner according to the apparatus disclosed in German Patent No. 30 08 606. In this latter patent, bearing portions are solid, non-resilient stones supported on and moved by special support and guide shoes against the associated crank pin, the bearing portion being made in the form of half-shells.
The use of guide shoes supported resiliently on tong-like guide arms determining the positioning of honing stones, carried at a different circumferential location on the tong-like guide arms, is known from German Offenlegungsschrift (Laid-Open Specification) No. 34 40 350. The honing stones are pressed against the respective crank pin by displacement cylinders which are provided in addition to an operating cylinder closing the guide arms relative to the workpiece in the manner of tongs.